<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
    var arr = [1,2,3,4];
    Array.prototype.getSum = function() {
        // console.log(this)
        var sum = 0;
        for(var i = 0; i < this.length; i++) {
            sum += i;
        }
        // console.log(sum)
        return sum;
    }
    Array.prototype = {
        sssss:"22222222222"
    }
    console.log(arr.getSum())

    </script>
</body>
</html>